U.S. patent number 10,313,994 [Application Number 15/172,254] was granted by the patent office on 2019-06-04 for variable synchronization block format.
This patent grant is currently assigned to TELEFONAKTIEBOLAGET LM ERICSSON (PUBL). The grantee listed for this patent is TELEFONAKTIEBOLAGET L M ERICSSON (PUBL). Invention is credited to Johan Axnas, Kumar Balachandran, Dennis Hui.
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United States Patent |
10,313,994 |
Balachandran , et
al. |
June 4, 2019 |
Variable synchronization block format
Abstract
An access node, AN, may be configured to communicate wirelessly
with a wireless device (WD). The AN can transmit a first
synchronization signal block having a first format. The AN can also
transmit a second synchronization signal block of a second format,
the first synchronization signal block including a first format
different from the format of the second synchronization signal
block. The first synchronization signal block can include an
extended primary synchronization signal block that can be used to
synchronize disadvantaged user equipment (e.g., user equipment
experiencing low signal-to-noise ratio).
Inventors: |
Balachandran; Kumar
(Pleasanton, CA), Axnas; Johan (Solna, SE), Hui;
Dennis (Sunnyvale, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
TELEFONAKTIEBOLAGET L M ERICSSON (PUBL) |
Stockholm |
N/A |
SE |
|
|
Assignee: |
TELEFONAKTIEBOLAGET LM ERICSSON
(PUBL) (Stockholm, SE)
|
Family
ID: |
53836127 |
Appl.
No.: |
15/172,254 |
Filed: |
June 3, 2016 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170094624 A1 |
Mar 30, 2017 |
|
Foreign Application Priority Data
|
|
|
|
|
Jun 15, 2015 [WO] |
|
|
PCT/IB2015/054522 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L
5/006 (20130101); H04W 72/085 (20130101); H04W
56/00 (20130101); H04L 43/16 (20130101); H04W
72/0446 (20130101); H04L 5/0007 (20130101); H04W
56/0015 (20130101) |
Current International
Class: |
H04W
56/00 (20090101); H04W 72/08 (20090101); H04W
72/04 (20090101); H04L 5/00 (20060101); H04L
12/26 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Yao; Kwang B
Assistant Examiner: Jeong; Moo
Claims
What is claimed is:
1. A method performed at an access node, AN, the AN configured to
communicate wirelessly with a wireless device (WD), the method
comprising: transmitting from the AN a first synchronization signal
block of a first format comprising an extended primary
synchronization signal and an extended secondary synchronization
signal for a first duration of time; and transmitting from the AN a
second synchronization signal block of a second format comprising a
primary synchronization signal and a secondary synchronization
signal for a second duration of time, the first duration of time
comprising a longer duration than the second duration, wherein the
AN is identified using an AN-ID that is one of a plurality of
unique AN-IDs, the plurality of unique AN-IDs being divided into a
plurality of groups, each group comprising a plurality of members,
such that each of the plurality of unique AN-IDs corresponds to a
specific group and a member of the specific group, wherein each of
the extended secondary synchronization signal and the secondary
synchronization signal indicates the same particular one of the
groups, and wherein each of the extended primary synchronization
signal and the primary synchronization signal indicates the same
one of the members of the particular group indicated by the
extended secondary synchronization signal and the secondary
synchronization signal, thereby communicating to the wireless
device, together with the particular group indicated by the
extended secondary synchronization signal and the secondary
synchronization signal, the AN-ID of the AN.
2. The method of claim 1, wherein the first synchronization signal
block activates the same beam two or more times.
3. The method of claim 1, wherein system-information is transmitted
adjacent in time or in frequency to one or both of the first
synchronization signal block and the second synchronization
block.
4. The method of claim 3, wherein the system-information
transmitted adjacent to the first synchronization signal block
contains information about the set of beams activated in the second
synchronization signal block.
5. The method of claim 4, wherein the information about the set of
beams activated in the second synchronization signal block includes
the number of times at least one of the activated beam are
repeatedly activated within the second synchronization signal
block.
6. The method of claim 3, wherein the system-information contains
the OFDM symbol number within a subframe.
7. The method of claim 1, wherein the first synchronization signal
block activates more beams per sector than the second
synchronization signal block.
8. The method of claim 7, wherein the second synchronization signal
block activates beams with a history of past WD detections.
9. The method of claim 7, wherein the second synchronization signal
block activates beams with a historic signal-to-noise ratio above a
threshold value.
10. The method of claim 7, wherein the second synchronization
signal block activates a subset of the beams activated by the first
synchronization signal block.
11. The method of claim 7, wherein the first synchronization signal
block comprises a primary synchronization signal and a secondary
synchronization signal, the secondary synchronization signal
activates beams having wider coverage than the beams activated by
the primary synchronization signal.
12. The method of claim 1, wherein the extended secondary
synchronization signal of the first synchronization signal block is
transmitted for a longer duration than the secondary
synchronization signal of the second synchronization signal
block.
13. An access node, AN, configured to communicate wirelessly with a
wireless device (WD) and comprising: a hardware processor; a
memory; and a transceiver; the AN configured to: transmit from the
AN a first synchronization signal block of a first format
comprising an extended primary synchronization signal and an
extended secondary synchronization signal for a first duration of
time; and transmit from the AN a second synchronization signal
block of a second format comprising a primary synchronization
signal and a secondary synchronization signal for a second duration
of time, the first duration comprising a longer duration than the
second duration, wherein the AN is identified using an AN-ID that
is one of a plurality of unique AN-IDs, the plurality of unique
AN-IDs being divided into a plurality of groups, each group
comprising a plurality of members, such that each of the plurality
of unique AN-IDs corresponds to a specific group and a member of
the specific group, wherein each of the extended secondary
synchronization signal and the secondary synchronization signal
indicates the same particular one of the groups, and wherein each
of the extended primary synchronization signal and the primary
synchronization signal indicates the same one of the members of the
particular group indicated by the extended secondary
synchronization signal and the secondary synchronization signal,
thereby communicating to the wireless device, together with the
particular group indicated by the extended secondary
synchronization signal and the secondary synchronization signal,
the AN-ID of the AN.
14. The access node of claim 13, wherein the first synchronization
signal block is transmitted with less periodicity than the second
synchronization signal block.
15. The access node of claim 14, wherein the first synchronization
signal block is transmitted once per transmission period and the
second synchronization signal block is transmitted at least twice
per transmission period.
16. The access node of claim 13, wherein the extended secondary
synchronization signal is located in a fixed relative location from
the extended primary synchronization signal.
17. The access node of claim 16, wherein the extended secondary
synchronization signal is located in a subframe that is transmitted
after a subframe in which the extended primary synchronization
signal is transmitted.
18. The access node of claim 16, wherein the extended secondary
synchronization signal comprises AN-specific pilot sequences.
19. The access node of claim 16, wherein the extended secondary
synchronization signal comprises a maximum length sequence
(MLS).
20. The access node of claim 13, wherein the first synchronization
signal block is phase offset from the second synchronization signal
block.
21. A method performed at a wireless device (WD), the WD configured
to communicate wirelessly with an access node (AN), the method
comprising: receiving from the AN a first synchronization signal
block of a first format comprising an extended primary
synchronization signal and an extended secondary synchronization
signal for a first duration; and receiving from the AN a second
synchronization signal block of a second format comprising a
primary synchronization signal and a secondary synchronization
signal for a second duration, the first duration being longer than
the second duration, wherein the AN is identified using an AN-ID
that is one of a plurality of unique AN-IDs, the plurality of
unique AN-IDs being divided into a plurality of groups, each group
comprising a plurality of members, such that each of the plurality
of unique AN-IDs corresponds to a specific group and a member of
the specific group, wherein each of the extended secondary
synchronization signal and the secondary synchronization signal
indicates the same particular one of the groups, and wherein each
of the extended primary synchronization signal and the primary
synchronization signal indicates the same one of the members of the
particular group indicated by the extended secondary
synchronization signal and the secondary synchronization signal,
thereby communicating to the wireless device, together with the
particular group indicated by the extended secondary
synchronization signal and the secondary synchronization signal,
the AN-ID of the AN.
22. The method of claim 21, wherein one or both of the first
synchronization signal block and the second synchronization signal
block repeatedly activate the same beam two or more times.
23. The method of claim 21, wherein a system-information block is
adjacent in time or in frequency to one or both of the first
synchronization signal block or the second synchronization
block.
24. The method of claim 23, wherein the system-information block
adjacent to the first synchronization signal block contains
information about the set of beams activated in the second
synchronization signal block.
25. The method of claim 24, wherein the information about the set
of beams activated in the second synchronization signal block
includes the number of times at least one of the activated beam are
repeatedly activated within the second synchronization signal
block.
26. A wireless device (WD) of a millimeter wave radio access
technology (mmW RAT) system, the WD configured to communicate
wirelessly with an access node (AN) and comprising: a hardware
processor; a memory; and a transceiver; the WD configured to:
receive from the AN a first synchronization signal block of a first
format comprising an extended primary synchronization signal and an
extended secondary synchronization signal for a first duration of
time; and receive from the AN a second synchronization signal block
of a second format comprising a primary synchronization signal and
a secondary synchronization signal for a second duration of time,
the first duration being longer than the second duration, wherein
the AN is identified using an AN-ID that is one of a plurality of
unique AN-IDs, the plurality of unique AN-IDs being divided into a
plurality of groups, each group comprising a plurality of members,
such that each of the plurality of unique AN-IDs corresponds to a
specific group and a member of the specific group, wherein each of
the extended secondary synchronization signal and the secondary
synchronization signal indicates the same particular one of the
groups, and wherein each of the extended primary synchronization
signal and the primary synchronization signal indicates the same
one of the members of the particular group indicated by the
extended secondary synchronization signal and the secondary
synchronization signal, thereby communicating to the wireless
device, together with the particular group indicated by the
extended secondary synchronization signal and the secondary
synchronization signal, the AN-ID of the AN.
27. The WD of claim 26, wherein the second synchronization block
activates beams with a historic signal-to-noise ratio above a
threshold value.
28. The WD of claim 26, wherein the second synchronization signal
activates a subset of the beams activated by the first
synchronization signal.
29. The WD of claim 26, wherein the first synchronization signal
block comprises a primary synchronization signal and a secondary
synchronization signal, the secondary synchronization signal
activates beams having wider coverage than the beams activated by
the primary synchronization signal.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to International Application No.
PCT/IB2015/054522, filed Jun. 15, 2015, the contents of which are
incorporated herein by reference.
FIELD
This disclosure pertains to variable synchronization block formats,
and more particularly, to variable synchronization block formats
for efficient beam-forming.
BACKGROUND
In networks that operate at high carrier frequencies, such as the
millimeter wave (mmW) band or in bands that are higher than those
used by conventional cellular networks such as Long Term Evolution
(LTE) and High Speed Packet Access (HSPA), the link between an
access node (AN) and the wireless device (WD) may depend on high
gain directivity to limit interference in the network and to
provide high signal-to-noise ratio (SNR) links.
FIG. 1 is a schematic illustration of beam finding resulting in
varying signal-to-noise ratios experienced by different wireless
device. The radios in the network may have varying capabilities.
FIG. 1 shows two established links from an AN to two WDs (WD1 with
high SNR and WD2 with low SNR) and several potential links to WDs
in the coverage area of the AN. The environment is prone to spotty
coverage and SNR can vary significantly between WDs. In addition,
WDs in the network can have varying capabilities such as the use of
analog vs. digital beam-forming. There is therefore a possibility
of widely varying SNRs between various links in the network.
SUMMARY
The use of spatial directivity can use signaling structure and
procedures for beam finding during initial access and handover.
This disclosure pertains to the definition of signaling structures
for synchronization signals, including synchronization signals for
such future systems, such as mmW Radio Access Technology systems
(or mmW RAT systems).
In general, beam-finding should occur in the shortest possible time
period, while at the same time, disadvantaged WDs should accumulate
enough energy from the synchronization signal without a burden of
subjecting other WDs to long beam-finding time periods.
This disclosure pertains to a design for the transmission of
synchronization sequences. The synchronization signals are
periodically broadcast by the AN. In embodiments, the AN can
broadcast the synchronization sequences using more than one format,
where at least one format is transmitted over a longer period of
time than the other single format or plural formats. The longer
synchronization blocks target users that have low SNR or are
disadvantaged in other ways such as restrictions like analog
beam-formers.
In embodiments, the AN can broadcast synchronization signals in at
least two groups, at least one over an extended time duration and
at least another in a short block period. In embodiments, the
shorter blocks can occur in multiple subgroups, some of which favor
beam patterns that are more prevalent from historical reports.
Embodiments may include repeating certain beam directions more
often that other beam directions to favor certain areas of
coverage. A further embodiment is directed to reordering beam
patterns to favor beams that are more frequently used.
In another embodiment of the invention, the longer blocks and the
shorter blocks can further include different numbers of repetitions
of the synchronization signal to allow receivers of different
capabilities to potentially find its own receive beam in the
appropriate direction.
Establishing links to each of the WDs in the coverage area will
proceed by timing synchronization signals in various directions,
allowing enough time for the WD in a particular direction to detect
the synchronization signal and to potentially train its own receive
beam in the appropriate direction.
Aspects of the present disclosure are directed to an access node
and methods performed by an access node (AN). The AN is configured
to communicate wirelessly with a wireless device (WD). The AN
includes hardware circuitry including a processor for executing
instructions, a memory for storing instructions and data, and a
transceiver for transmitting and receiving signals wirelessly via
one or more antennas. The processor can be a hardware processor
that can execute instructions stored on the memory. The AN can
transmit a first synchronization signal block for a first format
lasting a first duration of time. The AN can transmit a second
synchronization signal block of a second format lasting a second
duration of time. The first format is different from the second
format and the first duration is longer than the second
duration.
Aspects of this disclosure pertain to wireless device (WD). The WD
may include a hardware processor, a memory, and a transceiver. The
WD may be configured to receive from the AN a first synchronization
signal block of a first format lasting a first duration of time.
The WD may also be configured to receive from the AN a second
synchronization signal block of a second format lasting a second
duration of time, wherein the first synchronization signal block
comprising a first format different from the format of the second
synchronization signal block, and the first duration comprising a
longer than the second duration.
In some embodiments, the AN is part of a millimeter wave radio
access technology (mmW RAT). In some embodiments, the WD is
configured for and in operation within a mmW RAT.
In some embodiments, the second synchronization signal block
comprises a primary synchronization signal block and the first
synchronization signal block comprises an extended primary
synchronization signal block.
In some embodiments, one or both of the first synchronization
signal block and the second synchronization signal block repeatedly
activate the same beam two or more times (e.g., for beam training
at receiver or for energy collection for receivers with low
signal-to-noise ratio).
In some embodiments, a system-information block is transmitted
adjacent in time or in frequency to one or both of the first
synchronization signal block or the second synchronization
block.
In some embodiments, the system-information block transmitted
adjacent to the first synchronization signal block contains
information about the set of beams activated in the second
synchronization signal block
In some embodiments, the information about the set of beams
activated in the second synchronization signal block includes the
number of times at least one of the activated beam are repeatedly
activated within the second synchronization signal block.
In some embodiments, the system-information block contains the OFDM
symbol number within a subframe.
In some embodiments, the second synchronization signal block
activates more beams per sector than the first synchronization
signal block.
In some embodiments, the second synchronization block activates
beams with a history of past wireless device detections.
In some embodiments, the second synchronization block activates
beams with a historic signal-to-noise ratio above a threshold
value.
In some embodiments, the second synchronization signal activates a
subset of the beams activated by the first synchronization
signal.
In some embodiments, the secondary synchronization signal activates
beams having wider coverage than the beams activated by the primary
synchronization signal.
In some embodiments, the first synchronization signal block is
transmitted with less periodicity than the second synchronization
signal block.
In some embodiments, the first synchronization signal block is
transmitted once per transmission period and the second
synchronization signal block is transmitted at least twice per
transmission period.
In some embodiments, the first synchronization signal block of the
first format comprises an extended primary synchronization signal
and an extended secondary synchronization signal, the extended
secondary synchronization signal located in a fixed relative
location from the extended primary synchronization signal.
In some embodiments, the extended secondary synchronization signal
is located in a next subframe from the extended primary
synchronization signal in the first synchronization signal
block.
In some embodiments, the extended secondary synchronization signal
comprises AN-specific pilot sequences.
In some embodiments, the extended secondary synchronization signal
comprises a maximum length sequence (MLS).
In some embodiments, the first synchronization signal block is
phase offset from the second synchronization signal block.
Advantages of the embodiments described in this disclosure are
readily apparent to those of skill in the art. Among the advantages
include the advantage of getting the AN to settle into a search
procedure that favors a natural coverage area for the AN. The
technique acknowledges the wide variation in channel quality in the
coverage area and helps expedite synchronization of WDs in the
coverage area on the basis of most likely directions to find WDs.
In addition, the beam-finding performance of WDs with good SNR can
be improved while also allowing eventual synchronization with WDs
that are relatively disadvantaged.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of beam finding resulting in
varying signal-to-noise ratios experienced by different wireless
device.
FIG. 2 is a schematic illustration of transmit and receive
beam-forming in a mmW RAT network in accordance with embodiments of
the present disclosure.
FIG. 3 is a schematic illustration comparing the primary
synchronization signal and the secondary synchronization
signal.
FIG. 4 is a schematic illustration of an OFDM radio frame showing
the location of the primary synchronization signal and the
secondary synchronization signal.
FIG. 5A is a schematic diagram of a frame structure showing
extended synchronization signals in accordance with embodiments of
the present disclosure.
FIG. 5B is a schematic diagram of an extended synchronization
signal in accordance with embodiments of the present
disclosure.
FIG. 5C is a schematic diagram of a synchronization signal in
accordance with embodiments of the present disclosure.
FIG. 6 is a schematic diagram of a frame structure showing extended
primary and secondary synchronization signals in accordance with
embodiments of the present disclosure.
FIG. 7 is an example frame structure showing the extended
synchronization signals and unextended synchronization signals in
accordance to embodiments of the present disclosure.
FIG. 8 is a schematic diagram of beams enumerated by the extended
synchronization signal and beams enumerated by unextended
synchronization signals.
FIG. 9 is a process flow diagram for an access node for
transmitting extended synchronization signals in accordance with
embodiments of the present disclosure.
FIG. 10 is a schematic block diagram of an access node in
accordance with embodiments of the present disclosure.
FIG. 11 is a schematic block diagram of modules for an access node
in accordance with embodiments of the present disclosure.
FIG. 12 is a process flow diagram for a wireless device in
accordance with embodiments of the present disclosure.
FIG. 13 is a schematic block diagram of a wireless device in
accordance with embodiments of the present disclosure.
FIG. 14 is a schematic block diagram of modules for a wireless
device in accordance with embodiments of the present
disclosure.
DETAILED DESCRIPTION
This disclosure pertains to the design of synchronization blocks
from an access node (AN) that uses beam-forming to enable access by
wireless devices (WDs) or other communication equipment (such as
other ANs) in the vicinity of the AN. The disclosure considers a
scenario where the link between a AN and the WD depends on high
gain directivity from the AN (transmit beam-forming) and possibly
the WD (receive beam-forming) to limit interference in the network
and to provide high SNR links. In such systems, spatial directivity
may be used to overcome tight link budget at millimeter Wave (mmW)
frequencies. Moreover, multiple feasible beams are identified for
every link to overcome occasional obstacles.
FIG. 2 is a schematic illustration of transmit and receive
beam-forming in a mmW RAT network 200 in accordance with
embodiments of the present disclosure. The AN 202 in this network
200 is capable of forming high gain beams in various directions. A
typical synchronization procedure would involve the AN 202 sending
known pilot signals (or pilots) or signature sequences successively
in one or more directions in each transmission segment. Pilots may
include a set of predefined signals on predefined radio resources.
For example, the pilots may be transmitted on predetermined
frequencies at regular time intervals. The other node, which may,
for example be a wireless device (WD) 204, may detect and use these
signals as a reference to which it can aligns its own frequency
reference and timing. The WD could, in some instances, train its
receiver beam to identify the best directions from which to receive
the AN signal. The AN 202 or WD 204 may implement beam-forming
using analog techniques such as phase shifters to shift the
direction of the beams or using other techniques.
The performance of a communication link between the AN 202 and WD
204 depends on the amount of energy that can be transferred from
the transmitter to the receiver. There are essentially two ways to
close the link--transmitting a low power signal for a long period
of time to allow energy accumulation over the long period, or the
use of beam forming in a short period of time, but with the
advantage of high antenna gain over that short period, again
allowing adequate transfer of energy, which is the product of power
received and the time period of reception.
This disclosure pertains to a design for the transmission of
synchronization sequences. The synchronization signals are
broadcast by the AN 204. In embodiments, the AN 204 can broadcast
the synchronization sequences using more than one format, where at
least one format is transmitted over a longer period of time than
the other single format or plural formats. The longer
synchronization blocks target users that have low SNR or are
disadvantaged in other ways such as restrictions like analog
beam-formers.
The ANs of the mmW RAT network shown in FIG. 2 broadcast
synchronization signals periodically. The synchronization signals
may further be of more than one type such as a Primary
Synchronization Sequence (PSS) and a Secondary Synchronization
Sequence (SSS), following a structure that is similar to LTE, and
structured in a way to reduce search complexity for
beam-forming.
FIG. 3 is a schematic illustration 300 comparing the primary
synchronization signal (PSS) 302 and the secondary synchronization
signal (SSS) 304. As shown in FIG. 3, the PSS 302 is structured
differently from the SSS 304. There are n unique AN-IDs that are
divided into n.sub.2 groups of n.sub.1 members each. The PSS 302
includes AN member ID (n1 sequences), whereas the SSS 304 includes
the AN group ID (n2 sequences). The PSS 302 includes coarse
time-frequency estimates and coarse Tx/Rx beam ("sector")
identifiers; whereas the SSS 304 include finer time-frequency
estimates and finer Tx/Rx beam IDs.
The PSS is located in the last OFDM symbol of first time slot of
the first subframe (subframe 0) of radio frame. The PSS structure
and subframe location allows the WD to be synchronized on subframe
level. Typically, the PSS is repeated in subframe 5, which means
the WD can be synchronized on a 5 ms basis since each subframe is 1
ms. From PSS, the WD is also able to obtain physical layer identity
(0 to 2).
The SSS symbols are also located in the same subframe of PSS but in
the symbol before PSS. From SSS, the WD is able to obtain physical
layer cell identity group number, as described above.
FIG. 4 is a schematic diagram of an OFDM radio frame showing the
location of the PSS 302 and the SSS 304. The PSS 302 is transmitted
in the center frequency portion of an OFDM symbol every 5
milliseconds. The PSS 302 is mapped into the first 31 subcarriers
on either side of the DC subcarrier. Therefore, the PSS 302 uses
six resource blocks with five reserved subcarriers on each side. In
time division duplex (TDD) mode, the PSS is mapped to the third
OFDM symbol in subframes 0 and 5. In frequency division duplex
(FDD) mode, the PSS is mapped to the last OFDM symbol in slots 0
and 10.
As shown in FIG. 4, a secondary synchronization signal (SSS) 304 is
also transmitted. The SSS 304 is based on maximum length sequences
(m-sequences), which are pseudorandom binary sequences. Three
m-sequences, each of length 31, are used to generate the
synchronization signals. The SSS 304 is transmitted in the same
subframe as the PSS but one OFDM symbol earlier. The SSS 304 is
mapped to the same subcarriers (middle 72 subcarriers) as the PSS
302.
The PSS and SSS are defined in 3GPP TS 36.211. "Physical Channels
and Modulation." 3rd Generation Partnership Project; Technical
Specification Group Radio Access Network; Evolved Universal
Terrestrial Radio Access (E-UTRA). The division of the
synchronization signal into PSS and SSS in the 3GPP LTE
specification signals is designed to reduce the complexity of the
cell search process.
FIG. 5A is a schematic diagram of a frame structure showing
extended synchronization signals in accordance with embodiments of
the present invention. The regular, unextended PSS and SSS occur at
specific time frequency coordinates periodically. In FIG. 5A, the
PSS/SSS blocks 502 occur once per PSS period (T.sub.PSS 516), which
is every 5 subframes in FIG. 5A (though the periodicity can be
different depending on implementation choices). The PSS block 502
is shown in more detail in the inset and includes 1 PSS signal per
sector (PSS and 4 sectors per PSS block. The PSS block 502 also
includes basic system information (SI) 514.
FIG. 5B is a schematic diagram of an extended synchronization
signal in accordance with embodiments of the present disclosure.
The ePSS block 504 is shown to occur less often as the PSS block
502. In FIG. 5B, ePSS block 504 is shown to occur once for every 3
instances the PSS occurs. The ePSS block 504 can be set to occur
during an Extended PSS Period (T.sub.ePSS 518). In FIG. 5A, the
T.sub.ePSS 518 is shown to be equivalent to 20 subframes, but the
T.sub.ePSS 518 is an adjustable period. That is, the T.sub.ePSS 518
can be different from what is shown in FIG. 5A. The T.sub.PSS 516
and T.sub.ePSS 518 highlight the difference in periodicity between
the PSS 502 and ePSS 504: the PSS 502 occurs more often than the
ePSS 504.
Each ePSS block 504 extends over a longer period of time than the
PSS blocks 502, as shown in the insets in FIG. 5A (see FIG. 5B and
FIG. 5C). Specifically, FIG. 5A shows that ePSS block 504 lasts for
the duration of a whole subframe, while the PSS block 502 occurs
over a portion of a subframe.
FIG. 5C is a schematic diagram of a synchronization signal in
accordance with embodiments of the present disclosure. The PSS in
each sector is labeled as 506, 508, 510, and 512, respectively. As
can be seen in the insets on FIG. 5A, the ePSS block 504 repeats
PSS four times per sector (with four sectors) for low SNR WDs or
WDs that are otherwise disadvantaged. As shown from the inset (FIG.
5B) of ePSS block 504, each PSS signal 506, 508, 510, and 512 is
repeated four times, once per sector. The PSS block 502 of FIG. 5C
transmits one PSS per sector (PSS 506, 508, 510, and 512 are each
shown once in the inset for block 502).
The ePSS block 504 also includes basic system information 514,
which is shown in FIG. 5A and FIG. 5B to be transmitted over the
entire subframe. The PSS block 402 shows SI 514 transmitted only
for the duration of the subframe during which PSS is transmitted.
Basic System information (SI) 514 occurs as part of each ePSS block
504. The basic SI may contain: Network-specific info (e.g. Network
ID) Phase of hopping sequence OFDM symbol # # of RX beam scan per
TX beam in SSS
The PSS block 502 can be optionally frequency hopped to enable
frequency diversity (shown in FIG. 5A by the PSS frequency spacing
for each occurrence of the PSS 502 and ePSS 504).
Extended secondary synchronization signals (eSSS) may also be
transmitted. FIG. 6 is a schematic diagram of an eSSS block 604 in
accordance with embodiments of the present disclosure. As shown in
FIG. 6, the SSS block 602 shares a subframe with PSS block 502. The
ePSS block 504, however, occurs in a separate subframe than the
eSSS block 604, which occurs across multiple subframes in the
example shown in FIG. 6.
The ePSS block 504 scans over a larger number of beams. Each of
beams 606, 608, 610, 612, 614, and 616 are repeated during the eSSS
transmission so that a number of receive beams can be tested by WDs
in range. System information 618 is also transmitted during the
eSSS block 604. System information 618 for the eSSS block 604
includes one or more of the following: beam measurement report type
(BRMT), the number of Tx and Rx beam scan in RACH, and the pointer
to more system information (e.g., master information block
(MIB)).
The PSS are AN-specific and provides a set of sequences for the
activated sectors for the current synchronization period. The SSS
are located at a fixed relative location in time to the PSS and may
for example be composed of M-sequences. Similar properties would
apply to the ePSS and eSSS, respectively.
FIG. 7 is an example frame structure showing the extended
synchronization signals and unextended synchronization signals in
accordance to embodiments of the present disclosure. FIG. 7
illustrates a frame structure that activates 16 beams during the
ePSS, with the eSSS handling 3 beams for each of the ePSS beams for
receive beam training (for a total of 48 beams). The regular,
unextended PSS/SSS activates a smaller number of beams (in this
example, 4 beams for PSS and 3 SSS beams for each of the PSS beams,
for a total of 12 SSS beams).
The number of receive beam scan for each transmit beam in eSSS and
regular SSS may be different to serve receivers with different
capabilities. Further transmit and receive beam tuning can be
performed in a succeeding dedicated training mode between the WD
and the AN. This invention is not concerned with that function. The
PSS is AN specific and is a limited number of sequences, say 8,
that are reused by ANs in the network. Each PSS has a number of
associated SSS, say 256, and the PSS and SSS combination determine
timing and beam configuration. PSS/SSS sequences are optionally
staggered between adjacent access points by p=0, 1, or 2 subframes
to avoid collisions.
There are several ways by which beams can be activated within the
ePSS/eSSS and the regular, unextended PSS/SSS groups. Without loss
of generality, it is assumed that all of the ePSS can be enumerated
(although further grouping of beams activated by the ePSS can be
done). The regular, unextended PSS/SSS groups will in turn activate
a smaller subset of the total number of beams with the subsets
activated corresponding to one or more of the following categories:
a. Beams with a history of past WD detections b. Beams likely to
provide high SNR In each scenario, the regular, unextended PSS/SSS
can still be used for beams more likely to find WDs. For example,
the likelihood may be determined based on historical data of past
WD detections and/or WDs with high SNR (e.g., SNR above a threshold
value, which can be predetermined by the network or can be set
based on channel conditions).
Each regular, unextended PSS/SSS group might follow a different
strategy to providing synchronization services. In an embodiment,
each regular, unextended PSS/SSS group may focus on a subset of
likely beams in the governing ePSS/eSSS group. Alternatively, the
regular, unextended PSS/SSS might tradeoff directivity for wider
coverage per beam--this strategy would be more likely to pick up
WDs that have relatively better link SNR to the AN.
FIG. 8 is a schematic diagram of beams enumerated by the extended
synchronization signal and beams enumerated by unextended
synchronization signals. In FIG. 8, a subset of beams more
correlated with movement patterns that have been accumulated by an
AN. The ePSS/eSSS could enumerate a larger number of beams (e.g.,
to reach disadvantaged WDs, as described above), while the regular,
unextended PSS/SSS targets more likely beams. FIG. 8 illustrates
how each type of synchronization signal could be used. FIG. 8 is a
schematic 800 of a top down view of a covered corridor 802. Within
the corridor 802 could be an AN 808 that provides service for WDs
in the corridor 802. The ovals represent areas of signal
illumination by the AN 808. The shaded ovals (e.g., oval 806)
depict areas of illumination by the AN 808 that, for example, have
a history of following pedestrian patterns within coverage of the
AN 808. The shaded ovals 806, therefor, could be areas targeted by
regular, unextended PSS/SSS. The unshaded ovals 804 represent areas
where WDs experience low SNR or other issues that result in a
disadvantage (as discussed above). The shaded ovals 804, therefore,
could be targeted by ePSS/eSSS by the AN 808 to make up for the
disadvantage.
FIG. 9 is a process flow diagram 900 for an access node for
transmitting extended synchronization signals in accordance with
embodiments of the present disclosure. The AN can generate a first
synchronization signal block 504 of a first format, lasting for a
first duration (902). The AN can generate a second synchronization
signal block 502 of a second format, lasting for a second duration
(904). The AN can transmit a first synchronization signal block 504
of a first format, lasting for a first duration (906). In some
embodiments, the first synchronization signal block 504 includes
the ePSS and, in some embodiments, can also include the eSSS. The
AN can also transmit a second synchronization signal block 502 of a
second format lasting a second duration of time (908). In some
embodiments, the second synchronization signal block includes the
regular, unextended PSS, and in some embodiments, can also include
the regular, unextended SSS. The first synchronization signal block
504 includes a first format different from the format of the second
synchronization signal block. The first format may specify the
number of beams for the ePSS and may also specify the number of
corresponding beams for the eSSS (in some instances, the number of
beams activated is the same between the first and second
synchronization signal blocks; rather, the duration of active beams
is what is different, discussed in FIG. 6 and below). Additionally
or alternatively, the first format may also specify the number
and/or content of SI blocks 514 transmitted with the first
synchronization block. Additionally or alternatively, the first
synchronization signal block format may include more
synchronization signals per sector than the secondary
synchronization signal block. The first synchronization signal
block format may include more PSS per sector than the secondary
synchronization signal block (see, e.g., FIG. 5A and FIG. 5B)
and/or more SSS per sector than the secondary synchronization
signal block (see, e.g., FIG. 6).
The first duration corresponds to the amount of time needed to
transmit PSS 506-512 the determined number of times (in the case
shown in FIG. 5B, four times each). The first synchronization
signal block 504 is transmitted once per transmission period 518.
Put differently, a transmission period is defined for the first
synchronization signal block 504, which is adjustable by the AN or
by an operator of the network. The first synchronization signal
block is transmitted once during this transmission period 518,
whereas the second synchronization signal block 502 is shown to be
transmitted at least three times during the transmission period
518. More generally, the first synchronization signal block 504 is
transmitted a fewer number of times that the second synchronization
signal block 502.
In some embodiments, the AN retrieves historical data about
previous connections with WDs (910). The regular, unextended
PSS/SSS groups will in turn activate a smaller subset of the total
number of beams with the subsets activated corresponding to one or
more of the following categories:
a. Beams with a history of past WD detections
b. Beams likely to provide high SNR
In each scenario, the regular, unextended PSS/SSS can still be used
for beams more likely to find WDs. For example, the likelihood may
be determined based on historical data of past WD detections and/or
WDs with high SNR (e.g., SNR above a threshold value, which can be
predetermined by the network or can be set based on channel
conditions).
FIG. 10 is a schematic diagram of an example access node 1000
according to embodiments of the present disclosure. As shown in
FIG. 10, the access node 1000 includes a processor circuit 1020, a
memory 1080, a transceiver 1040, and an antenna 1060. The memory
1080 can store instructions that can be executed by the processor
1020. The memory 1080 can also store functional modules 1100, which
are described in more detail in FIG. 11. The memory 1080 can also
store information pertaining to historical data of connected WDs,
the locations of WDs when they were connected to the AN,
indications of SINR/SNR or other channel conditions for specific
beams, etc.
In particular embodiments, some or all of the functionality
described above as being provided by a base station, a node B, an
enhanced node B, and/or any other type of network node may be
provided by the node processor executing instructions stored on a
computer-readable medium, such as the memory shown in FIG. 10.
Alternative embodiments of the radio access node may include
additional components responsible for providing additional
functionality, including any of the functionality identified above
and/or any functionality necessary to support the embodiments
described herein.
In embodiments, the access node may be a base station, a node B, an
enhanced node B, and/or any other type of network node may be
provided by the node processor executing instructions stored on a
computer-readable medium, such as the memory shown in FIG. 10.
Alternative embodiments of the radio access node may include
additional components responsible for providing additional
functionality, including any of the functionality identified above
and/or any functionality necessary to support the solution
described above.
FIG. 11 is a schematic block diagram of functional modules 1100 of
an access node in accordance with embodiments of the present
disclosure. The functional modules 1100 can include a module for
generating synchronization signal blocks 1120, such as first
synchronization signal block 504 and second synchronization signal
block 502. The functional modules 1100 can also include a module
for transmitting synchronization signal blocks 1140, such as first
synchronization signal block 504 and second synchronization signal
block 502.
FIG. 12 is a process flow diagram 1200 for a wireless device in
accordance with embodiments of the present disclosure. The WD
receives, from an access node, a first synchronization signal block
having a plurality of synchronization signals per sector (1220).
The WD synchronizes with the access node (1240). In embodiments,
the WD trains the receiver beam to detect synchronization signals
from a certain direction. The WD can use positioning information as
well as historical information about the location and previous
connections (from the WD itself or from other WDs) to identify how
and where to train the receiver beam. In embodiments, the WD is a
disadvantaged WD, and the synchronization signal is an enhanced
primary synchronization signal and/or enhanced secondary
synchronization signal.
FIG. 13 is a schematic block diagram of a wireless device 1300 in
accordance with embodiments of the present disclosure. As shown in
FIG. 13, the example wireless device includes a processor circuit
1320, a memory 1380, a transceiver 1340, and an antenna 1360. In
particular embodiments, some or all of the functionality described
above as being provided by WDs, MTC or M2M devices, and/or any
other types of wireless communication devices may be provided by
the device processor executing instructions stored on a
computer-readable medium, such as the memory shown in FIG. 13.
Alternative embodiments of the wireless communication device may
include additional components beyond those shown in FIG. 13 that
may be responsible for providing certain aspects of the device's
functionality, including any of the functionality described above
and/or any functionality necessary to support the solution
described herein.
The WD 1300 is configured to receive synchronization signals and
synchronize with an access node, such as access node 1000. The WD
may be a disadvantaged WD. That is, the WD may experience low
signal to noise ratio may have other characteristics or may be in a
location that makes it difficult to connect to an access node. The
WD may train its transceiver 1340 to connect search for
receive-beams from certain directions. The transceiver 1340 may
also be configured to search for synchronization signals over a
larger time interval (specifically, for a period T.sub.ePSS, which
is a predetermined time period defined by the network or is
dynamically established by the access node or WD when the WD is
disadvantaged).
In embodiments, the WD may be a user equipment (UE), such as a
mobile handset, tablet PC, cellular phone, smart phone, or other
device. The WD may also include machine-type communication devices
(so-called MTC devices), M2M devices, and/or any other types of
wireless communication devices may be provided by the device
processor executing instructions stored on a computer-readable
medium, such as the memory shown in FIG. 13. Alternative
embodiments of the wireless communication device may include
additional components beyond those shown in FIG. 13 that may be
responsible for providing certain aspects of the device's
functionality, including any of the functionality described above
and/or any functionality necessary to support the solution
described above.
The WD memory 1380 is configured to store instructions executed by
the processor circuit 1220. The memory 1380 can also store
functional modules 1400. FIG. 14 is a schematic block diagram of
functional modules in accordance with embodiments of the present
disclosure. Functional modules 1400 include a synchronization
module 1420 configured to synchronize the WD with the access node.
The synchronization module can configure the WD to adapt the WD
transceiver to search for synchronization signals over a larger
period of time, as described above.
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